1. Field of the Invention
This invention relates generally to pistons, including light vehicle diesel pistons for internal combustion engines, and methods for manufacturing the same.
2. Related Art
Pistons used in internal combustion engines typically include an upper piston part joined to a lower piston part. Various methods are known for joining the piston parts together. One common joining technique is friction welding, which includes continuously rotating at least one of the piston parts about its center axis at a high speed and under pressure against the other piston part. However, friction welding is known to create a significant amount of flash or scrap material in the cooling chamber of the piston, as well as residual stress and/or cracking along the weld. Resistance welding and laser welding have also been used to join piston parts together. However, these joining methods are known to cause residual stress, inadequate strength, and/or cracking along the weld. Another joining technique includes induction welding the piston parts together. An example of this technique is disclosed in U.S. Pat. Nos. 6,825,450, and 7,005,620. However, there is still a need for strong welded pistons produced with less flash and scrap material, as well as less residual stress and cracking along the weld.